Challenges are encountered when plastic spunbonded filaments are melt extruded from a synthetic resin to form a spunbonded nonwoven fabric. Ordinarily a large number of threads are extruded from a single extrusion head, and among the challenges that are encountered are obtaining uniform thread size, uniform temperature across the whole of the extrusion head, and uniform flow distribution and pressure on extrusion orifices or spinnerettes. It would be desirable to provide an apparatus and a method of extruding a large number of fibers that provides uniform flow and temperature to the polymer composition from which the fibers are extruded and that imparts the same processing conditions and processing history to the melted polymer compositions at similar positions in the melt extrusion process. The spinnerettes may be single orifice spinnerettes for monofilament threads or groups of orifices to produce a multi-filament thread. Spinnerets are well known and are described and illustrated in U.S. Pat. No. 4,445,833.
An early attempt to extrude improved melt extruded threads was suggested in U.S. Pat. No. 3,057,009 to Lipski. Lipski describes an extrusion head in which melted synthetic resin is moved in the form of a relatively extended sheet to a series of orifices or spinnerettes which are a series of needles with hollow channels. Lipski utilizes a series of constrictions and expansions in the final channels to the extrusion orifices to distribute the molten resin to the needles. Lipski represented an improvement in the art but does not provide a distribution system that provides uniform processing time, temperature and history to processed polymer resin across the extrusion head.
Another attempt to solve the problems is presented in U.S. Pat. No. 3,381,336 to Wells.